A study conducted by the National Institute on Drug Abuse found using marijuana and alcohol together impacts driving more than using either substance alone, Time reports.
The study included 18 occasional marijuana smokers—13 of them men—between the ages of 21 and 37. They took six 45-minute drives in a driving simulator.
Before using the simulator, participants consumed specific combinations of marijuana and alcohol, or a placebo. They used a vaporizer to consume marijuana because the study took place at the University of Iowa, which is smoke-free. The study participants gave blood and saliva samples so researchers could verify their intoxication levels. The researchers measured their levels of THC (the psychoactive chemical in marijuana) and their blood alcohol concentrations.